One way to generate an image of the interior of an opaque structure makes use of a phenomenon known as nuclear magnetic resonance (NMR). Generally, NMR is a phenomenon by which atoms absorb energy provided from an external magnetic field, and subsequently radiate the absorbed energy as photons. By controlling the magnetic field throughout a region, one can control the frequency and phase of the emitted photons to vary as a function of the emitting atom's position in the region. Therefore, by measuring the emitted photons' frequency and phase, one can tell where the atoms are present inside the region.
In FIG. 1, one way to represent the data gathered from the resonant atoms is by constructing a k-space dataset 100. Each radiated photon is characterized by its wave number (often denoted k) or equivalently its frequency, and its phase relative to a reference phase. The k-space dataset 100 is a plot of the number of photons detected with a particular wave number and a particular phase. Often, k-space dataset 100 is represented as a two-dimensional array of pixels that have varying intensities. Dark pixels indicate that a relatively small number of photons were detected at the particular wave number and phase, and bright pixels indicate that a relatively large number of photons were detected at the particular wave number and phase.
An image 102 can be reconstructed from the k-space dataset 100 by various mathematical techniques. These techniques are useful for imaging the internal structure of a human being. In this context, the hydrogen atoms that make up the human's body are caused to undergo nuclear magnetic resonance. In the context of imaging the hydrogen in a human or other animal, this technique is sometimes referred to as magnetic resonance imaging (MRI). Since hydrogen is present in nearly every organ, tissue, fluid, or other part of a human being. MRI typically provides a relatively detailed image of the human being through non-invasive means.
In some MRI contexts, it is desirable to quickly acquire the k-space data necessary to produce an image. For example, when imaging a patient's heart, the image quality is often enhanced if the patient suppresses respiratory-induced motion by holding his breath while the k-space data is acquired. Some patients experience discomfort or difficulty holding their breath for extended periods of time, particularly patients who are in need of cardiac imaging.
One way to reduce the time required to acquire the k-space data is to employ multiple detectors, with each detector configured to detect photons from different spatial regions. This approach is referred to as “parallel” MRI, or pMRI.